Electromagnetic relay is one of the earliest and most widely used relays. Electromagnetic relay usually consists of iron core, electromagnetic coil, armature, return spring, contact, bracket and pin.

The working principle of Electromagnetic relay is not simple. It mainly uses the principle of electromagnetic induction. When a current is applied to the coil, the coil generates a magnetic field, and the iron core under the coil is magnetized to generate a magnetic force, so the armature is attracted to the iron core under the action of electromagnetic attraction. At this time, the armature drives the support rod to push the leaf spring open, thereby opening the two normally closed contacts. When the current of the relay coil is disconnected, the iron core loses its magnetism, the armature returns to its initial state under the action of the leaf spring, and the contact is closed again.

The forms of contacts are usually divided into three types: one is a static contact that is in a conducting state when the relay coil is not energized, which is called a normally closed contact and is represented by the letter H; the second is an open state. Static contacts, called normally open contacts, are represented by the letter D; the other is that the moving contacts and the static contacts are normally closed, and at the same time they are normally open with the static contacts to form an open-close conversion contact form, which is represented by the letter I. express. When the coil is energized, the normally closed contact is disconnected by the closed state, so it is also called a dynamic breaking contact, and the normally open contact is called a dynamic closing contact.